micro-oxygenation in contemporary winemaking - Cape Wine ...

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Micro-oxygenation in Contemporary Winemakingas sherry and port. Lastly, there is a rapidly growing literature on the anti-oxidant role ofphenolic compounds and their potential health benefits, but again this will be consideredonly very briefly in relation to the potential impact of micro-oxygenation on wine anti-oxidantcapacity.1.2 CONTRIBUTION OF THE REPORTThe purpose of this review is to provide an up-to-date description and synopsis of microoxygenation.There are a number of excellent and relatively recent reviews on winephenolic chemistry (Monagas et al., 2005; Fulcrand et al., 2006; Ribéreau-Gayon et al.,2006c; Parker et al., 2007) and the role of oxygen in winemaking (du Toit et al., 2006b;Danilewicz, 2007; Li et al., 2008), but the intended contribution of this report is to presentthis somewhat technical material for a practitioner, rather than an academic audience.Another key objective of the report is to summarise the latest available scientific evidenceon the benefits and risks of micro-oxygenation. Although there are a number of generalreviews on micro-oxygenation (Parish et al., 2000; Zoecklein et al., 2002; Blackburn, 2004;Pour-Nikfardjam and Creasy, 2004; Goode, 2005), none of these are very recent and fewprobe beyond the broad assertions of the micro-oxygenation industry. Although a numberof more rigorous studies of micro-oxygenation have been published in the last few years(del Carmen-Llaudy et al., 2006; Cano-López et al., 2006; du Toit et al., 2006a; Pérez-Magariño et al., 2007), a systematic review of this evidence has not yet been produced.1.3 OUTLINE OF THE REPORTThis report is broadly divided into four main parts. Part I (Chapters 1 – 3) outlines thethemes to be explored in this report and introduces the micro-oxygenation technique byproviding a definition and brief history. Part II (Chapters 4 – 5) describes the commercialclaims and practical application of micro-oxygenation. Part III of the report (Chapters 6 – 7 )reviews the available scientific evidence concerning the relevant chemical reactions as wellas the proven advantages and disadvantages of micro-oxygenation. Finally, Part IVprovides some general conclusions and recommendations.4
Micro-oxygenation in Contemporary WinemakingCHAPTER 2: DEFINING MICRO-OXYGENATIONThe focus of this report is on the technique known as micro-oxygenation. However, thereare a number of terminological and definitional issues that need to be clarified becausedifferent writers and disciplines use different terminology and definitions. That is thepurpose of this short introductory chapter.In this report micro-oxygenation will be simply defined as “the intentional and controlledaddition of small measured amounts of oxygen to wine” (Paul, 2002). Oxygenation usuallyrefers to the deliberate exposure of wine to oxygen and implies a positive impact on winequality. In contrast, the term oxidation (or oxidised) is more frequently associated with thenegative consequences of excessive oxygen exposure (Blackburn, 2004). Chemists,however, use the words oxidation and reduction simply to describe the exchange ofelectrons in redox reactions.Micro-oxygénation was the phrase coined when the technique was developed in Franceand micro-oxygenation is still the most common usage. Aeration and micro-aeration aresometimes used as synonyms for oxygenation and micro-oxygenation, though strictlyaeration means exposure to air whereas oxygenation implies treatment with pure oxygen.In practice, however, both terms are used for both air and pure oxygen exposure. Microbullageis another synonym which invokes the characteristic bubbling of oxygen but thisterm is not in widespread use and, in fact, more modern equipment strives to make thebubbles as small and unobtrusive as possible.Micro-oxygenation is generally accepted as being the deliberate introduction of oxygen andinvolving the use of specialised equipment to regulate the doses of oxygen that areadministered. So the term does not usually include the passive oxygen exposure thatoccurs during barrel ageing nor the range of winemaking practices – such as pumpingover, topping up and racking – where oxygen exposure may be intentional but is not wellmeasured (Rieger, 2000).However, there is less consensus on how low the dose needs to be to qualify as microoxygenation(Paul, 2002), whether or not the oxygen treatment has to be continuous(Jones et al., 2004), and if micro-oxygenation can only be used if exposure happens over along period of time (Waterhouse, 2004). For example, a number of authors use macrooxygenationto refer to the higher dose exposures (in the order of 2-4 mg/L/day) of fairly5
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